I wanted to come back and share what I have found. I have been looking at this issue for the last few days and I have easily come across 20 posts sharing the link I provided above. Each of these posts discusses getting the DHCP Relay to work with PFsense while using an IPSec tunnel. One thread referenced here:
https://forum.pfsense.org/index.php?topic=6932.0
States that ssheikh back in 2008 actually got this to work by providing a dummy route back toward the DHCP relay machine from the other end of the IPSec link, but I have not been able to reproduce this.
Finally, in an effort to solve this, I submitted a support ticket. In which I received the reply:
I have discussed your case whit our engineers and what you are trying to do here simply dose not work within pfSense alone, to achive this you need to use the IP Helper and DHCP Relay on the switches not on pfSense as it do not manage to send the reply back to the client, however you can still use the IPSec tunnel on pfSense
So unless someone has something to add here, this simply won't work at all. HOWEVER….
I also found this thread:
https://forum.pfsense.org/index.php?topic=57769.0
That apparently allows you to pull in another DHCP relay package. This package will allow you to bind to an IP address on the local pfsense box. I found another thread referencing this and saying it functions well. So this might deserve some follow up if you are really interested in making this work.